1. Field of the Invention
This invention relates to lasers; and more particularly, to a high power, solid-state laser having a shielded laser cavity insert.
2. Description of the Prior Art
Laser producing reactors of the type upon which this invention has improved are typically solid-state optical pumping lasers wherein an alexandrite lasing medium is surrounded by transparent fused silica. The transparent fused silica is, in turn, surrounded by a reflector chamber containing a reflective powder, such as barium sulfate. One of the most troublesome problems with operation of these lasers is the tendency of coolant water to leak into the reflector chamber. Such leakage is generally occasioned when degradation of the laser""s O-ring water seals permits coolant to seep past or around the seals. Once inside the reflector chamber, the coolant deteriorates the barium sulfate laser light reflectors, and prevents proper lasing of the device.
To resolve the leakage problem, it has been proposed that metal O-rings be used to enhance stability and avoid O-ring degradation. Such metal O-rings require substantial pressure to effect an appropriate seal, which can fracture the fused silica laser cavity insert wherein the laser rod and flashlamps are housed. Also proposed for this purpose were carbon seals. The carbon seals lost their compression shortly after installation. Coolant leaked around and through the seals, entered the reflector chamber and caused rapid deterioration of the reflector material, typically barium sulfate, contained therein.
Alternative structures proposed to resolve the leakage problem include use of gold or silver coated mirror reflectors (see U.S. Pat. No. 4,894,837 to DiFonzo, et al.; U.S. Pat. No. 5,422,899 to Freiberg, et al.; U.S. Pat. No. 4,232,276 to Iwata) or reflectors adapted to withstand water contact (see U.S. Pat. No. 5,299,213 to Kuba, et al.; U.S. Pat. No. 4,858,243 to Bar-Joseph). These mirror reflectors are oftentimes scratched during routine maintenance, reducing their reflectivity. In addition, water impurities tend to tarnish or deposit film on the reflectorsxe2x80x94whether comprised of Macor ceramic material or a coated mirror-type surfacexe2x80x94reducing lazing efficiency. Use of alternative cooling mechanisms such the heat sink taught by U.S. Pat. No. 4,096,450 to Hill, et al., result in less efficient cooling which restricts power output and efficiency of the laser. When compared to these alternate laser designs, solid state pumping lasers that are water-cooled and utilize reflector chambers packed with material such as barium sulfate, have retained popularity, especially for high-power laser applications.
A major contributor to O-ring seal deterioration in water-cooled lasers is the ultraviolet light produced during pumping of the flashlamps as the laser rod is caused to laze. In order to optically pump the laser to peak power at which the flashlamps cause the laser rod to laze and otherwise perform, a reflector is required. The reflector is typically created by packing barium sulfate as a reflector within a reflector chamber, formed between the internal facing of a laser cavity housing and the periphery of the laser cavity structure. The barium sulfate reflector intensifies the light produced by the high intensity flashlamps. It also causes rapid degradation of water seals, including the O-ring seals, and leakage of coolant water therethrough. The leaking water seeps into the reflector chamber, deteriorating the barium sulfate reflector and impairing operability of the laser.
There remains a need in the art for a solid-state optical pumping laser which can be run at high power in an efficient, reliable manner. Particularly needed is a solid-state optical pumping laser that can be efficiently cooled without degradation of water seals and reflector deterioration.
The present invention provides a solid state optical pumping laser which can be pumped to high power and run at that high power level for a prolonged period of time in an economical, efficient and highly reliable manner. Generally stated, the solid-state optical pumping laser has a housing (referred to hereinafter as laser pump chamber) for defining a cavity containing a laser light producing space and a coolant flow space. The pumping chamber casing has at least one channel therewithin for coolant flow contiguous with the light-producing space. At least one flashlamp is operatively mounted within the light producing space. Mounted on the pumping chamber casing exterior to the coolant flow space and to the light producing space is at least one laser rod composed of non-conductive, crystalline material. The pumping chamber further includes a reflective material composed of a major amount of barium sulfate for reflecting flashlamp light into the laser rod to maximize reflected flashlamp concentrated light. A coolant structure having at least one coolant flow-channel is provided for directing water-containing coolant to and from the coolant flow space. The pumping chamber has a sealing means for isolating the reflective material from coolant within said coolant flow space. Such sealing means includes at least one water barrier seal for physically sealing the coolant flow space against leakage of the water-containing coolant to thereby prevent coolant contact with the reflective material. Protection against deterioration caused by contact with the water-containing coolant is thereby afforded to the reflective material. A barrier means blocks substantially the entire amount of ultraviolet radiation emitted by the flashlamp from contacting the sealing means. The barrier means thereby prevents deterioration of the sealing means caused by exposure to the ultraviolet radiation.
More specifically, the invention provides a solid-state optical pumping device wherein reflective surfaces are effectively isolated from the coolant water, preventing contact of coolant-water with the barium sulfate powder. Degeneration of reflectors and diminution of lasing magnitude is eliminated. The water seals are shielded from substantially all light (including ultraviolet light) from the flashlamps by at least one and preferably a plurality of ultraviolet radiation barriers. With this arrangement, ultraviolet light from the flashlamps is prevented from striking the water seal(s), such as the O-ring water-leakage barriers; and water leakage-contact with barium sulfate powder extant within the reflector chamber is avoided.
In a first preferred embodiment, an ultraviolet radiation barrier comprises at-least a major and effective amount of opaque fused silica. Such opaque fused silica is present in an amount and a thickness sufficient to substantially block passage of ultraviolet radiation therethrough. With this arrangement, deterioration of the water barrier seal is substantially completely prevented, or is reduced at-least to a degree sufficient to prevent leakage of water-containing coolant in an amount sufficient to reach and destroy or degrade the barium sulfate reflector.
Preferably, the ultraviolet radiation barrier comprises a substantially linearly extending rigid sheet. More preferably, the substantially rigid sheet is composed of opaque fused silica. The ultraviolet radiation barrier can further include at-least an amount of opaque fused silica sufficient to block ultraviolet radiation from contacting the sealing means. At-least two separate spaced-apart sections of the ultraviolet radiation barrier are positioned, respectively, at an inlet end and an outlet end of an at-least one lamp mounting and coolant flow space and of an at least one substantially laser rod enclosing and coolant flow space. The ultraviolet radiation barrier includes at-least one through-space opening disposed in alignment with at least one of the inlet end and the outlet end of the lamp mounting and coolant flow space and the laser rod enclosing and coolant flow space.
The ultraviolet radiation barrier can also comprise at least two spaced-apart, substantially linearly extending sheets. One of the sheets is thermally fused to a cavity structure adjacent to the inlet end. Another of the sheets is thermally fused to the cavity structure at the outlet end. Preferably, each of the ultraviolet radiation barriers comprises a substantially linearly extending sheet. More preferably, each of the linearly extending sheets is composed of fused silica.
Each of the ultraviolet radiation barriers includes at-least one portion alignable with at least a portion of light producing and coolant flow spaces. In addition, the ultraviolet radiation barriers are positioned, respectively, at an inlet end and an outlet end of the light producing and coolant flow space and the laser rod enclosing and coolant flow space. The ultraviolet radiation barriers include at-least one through-space opening disposed in alignment with the inlet end and the outlet end of the light producing and coolant flow space and the laser rod enclosing and coolant flow space.
The ultraviolet radiation barrier preferably comprises at-least two spaced-apart substantially linearly extending sheets. One of the sheets is thermally fused to cavity structure adjacent to the inlet end. Another of the sheets is thermally fused to cavity structure at the outlet end. A major and effective amount of glass-to-metal sealing and low expansion alloy, such as Invar, molybdenum and the like, having a coefficient of thermal expansion substantially the same as glass, is contained by the barrier. Whether the spaced-apart substantially linearly extending sheets of which the ultraviolet radiation barrier is comprised are formed from glass-to-metal sealing and low expansion alloy or are formed from opaque fused silica glass, they are in each case thermally fused to the transparent fused silica cavity structure.
The amount and thickness of the glass-to-metal sealing and low expansion alloy is sufficient to substantially block the ultraviolet radiation. With this arrangement, the water barrier seals are precluded from deteriorating; and leakage of water-containing coolant in an amount sufficient to reach and destroy the barium sulfate reflector is prevented. The seal is preferably composed of cerium-doped glass having a thickness sufficient to substantially block passage of ultraviolet radiation therethrough. The shield thus provided prevents deterioration of the water barrier seal which, in turn, prevents leakage of water-containing coolant into the reflector chamber in sufficient amount to reach and diminish the reflective characteristics of the barium sulfate powder.
The at-least a major and effective amount of aluminum oxide ceramic preferably has a density ranging from about 3.7 to 3.8 grams per cubic centimeter. Aluminum oxide ceramic is present in an amount and thickness sufficient to substantially block passage of the ultraviolet radiation therethrough. The water barrier seal is thereby precluded from becoming deteriorated, and remains operative to prevent leakage of water-containing coolant into the reflector during extended pumping of the laser for a prolonged period of time. In an alternative embodiment of the invention, the aluminum oxide ceramic is replaced by molybdenum, present in an amount and thickness that passage of ultraviolet radiation through the ultraviolet radiation barrier is substantially prevented.
At least a major and effective amount of smokey quartz can, alternatively, be employed in place of the molybdenum. The amount and thickness of smokey quartz used is sufficient, in combination, to substantially block passage of the ultraviolet radiation through the barrier. Use of the ultraviolet radiation barrier prevents deterioration of the water barrier seal and leakage of water-containing coolant in an amount sufficient to reach and destroy barium sulfate reflector.
Significant structural and operational advantages are incorporated into the elements of this invention. Cooling efficiency is optimized and sealing of the reflectors is accomplished in a highly reliable manner. Leakage of coolant around and through the water seals is virtually eliminated. The reflector is isolated from leakage of coolant water and ultraviolet light is blocked from reaching the water coolant seals. Degradation of the water seals is minimized and the laser rod and flashlamps are efficiently and reliably cooled. Lasing is effected at higher efficiency and with less disruption than solid state pumping lasers in which barium sulfate is cooled by a heat sink, or in which water contacts gold, ceramic or silver reflectors.